Originally Posted by Teemō
They can be separated. There are a few services in Asia which do this specifically for vintage lenses. I don't know about cost, I'll get a quote, but so far at least one business doesn't appear to have dealt with any 35/1.7's in over 5 years of business, but plenty of 50/1.1 Noktons and 75/90mm CV's. I can't find any reference to the 35/1.7 having cement issues but it appears fairly common in their other lenses. I am seeing quite a few 35/2.5's with similar mild haze. I'm thinking it's condensation due to humid storage conditions. I don't think that would occur between a doublet that doesn't have cement issues, but it could still be between individual elements of the optical block (despite that they are sealed).
The way I see (hope) it is, the haze has got a good chance of only being on the surfaces directly adjacent to the aperture - they are most exposed to penetration throughout the rest of the lens. Because of the number of CV lenses with haze or cement issues, I'm not exactly full of confidence that the issue won't just develop in the future, if the conditions are right.
This is very surprising. I had conversations about seperation and cements with John Van Stelton (Focal Point) in the U.S. before he retired. John was the last "great" lens repair shop on this continent. Yes, SK Grimes are good too, but are reluctant to work on lenses of interest to me... except for my LF lenses.
Most modern lenses with UV cemented groups require substantial effort and nasty chemicals to separate. Older lenses that used balsam can be separated more easily, and then it becomes a matter of how practical the access will be (e.g., the Leica 90/2.8 elmarit v1). According to John, the effort and time required to repair a lens requiring separation of UV cemented elements can lead to a cost greater than the lens, sometimes much greater. He seemed to suggest it is most practical for lenses that are rare or special. And that's considering the separation part, lens disassembly, cleaning, reassembly, collimation can be difficult too -- especially modern zoom lenses, but luckily we're talking lovely little RF lenses here
I suppose I would like to know more about the shops you mentioned. I have lenses with separation issues that I would like to repair, but not spend a fortune in doing so. I repair most of my own balsam-cemented issues, but not the others. Methylene chloride was just banned from consumer use in the U.S. and it was banned in the E.U. (and U.K. now) a while ago. In any case, if cost is reasonable at the shops you mentioned, shipping to/from Asia is not a barrier.
Oddly enough, I seem to have a small can of Methylene chloride in my shop. Can't remember why I have it. Better hold on to it because I can't get more. According to the press release I read, the reason for banning consumer sale of MeCL2 is due to the high number of people using the product in a non-ventilated space -- exactly what the instructions on the label tell you NOT to do -- Usually in all caps.
Are we being saved from ourselves? Or thwarting natural selection?